In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, carbon dioxide CO2. With increasing environmental demands various processes for removing carbon dioxide from the process gas have been developed. One such process is the so called oxy-fuel process. In an oxy-fuel process a fuel, such as one of the fuels mentioned above, is combusted in the presence of a nitrogen-lean gas. Oxygen gas, which is provided by an oxygen source, is supplied to a boiler in which the oxygen gas oxidizes the fuel. In the oxy-fuel combustion process a carbon dioxide rich flue gas is produced, which can be disposed of in order to reduce the emission of carbon dioxide into the atmosphere.
Prior to being disposed of, it is necessary to clean the carbon dioxide gas. WO 2010/021053 discloses a gas cleaning system in which a hot process gas generated in a boiler is subjected to removal of nitrogen oxides, dust, and sulphur dioxide. The hot process gas, being a carbon dioxide rich gas, is then subjected to a mercury removal step to clean the carbon dioxide rich gas prior to the disposal thereof.